Chloromethylated polystyrene cross-linked with divinylbenzene and grafted with vanadium(IV) and vanadium(V) complexes having ONO donor ligand for the catalytic activity

Article abstract of DOI:10.1016/j.molcata.2013.12.006

The ligand H₂sal-iah (I), derived from salicylaldehyde and indole-3-acetic hydrazide, reacts with [V^IVO(acac)₂] in methanol to give oxidovanadium(IV) complex [V^IVO(sal-iah)(H ₂O)] (1). In the presence of KOH, arial oxidation of 1 in methanol yields dioxidovanadium(V) complex K[V^VO₂(sal-iah)] ·H₂O (2). Complex 1 has been grafted via covalent bonding through imino nitrogen of the indole group to chloromethylated polystyrene cross-linked with 5% divinylbenzene {now abbreviated as PS-[V ^IVO(sal-iah)(H₂O)] (3)}. Its oxidomethoxido vanadium(V) analog {PS-[V^VO(OMe)(sal-iah)] (4)} can be obtained by aerial oxidation of methanolic suspension of 3. All these complexes are characterized by various spectroscopic techniques (IR, electronic, ¹H and ⁵¹V NMR, electron paramagnetic resonance (EPR) and thermal as well as field-emission scanning electron micrographs (FE-SEM)) studies. The EPR spectrum of 3 indicates that the magnetically dilute V^IVO-centers are well dispersed in the polymer matrix while EPR spectrum of 1 shows slightly different binding mode around vanadium center. ¹H and ⁵¹V NMR spectra of 2 are compatible with the existence of expected dioxide species as the major product and oxidomethoxido species as a minor component in solution. Independent of the species presents in methanol, complexes 1 and 2 upon treatment with H₂O₂ both change to same oxidoperoxido species. The polymer-grafted complex 4 catalyzes the oxidation, by H ₂O₂, of styrene and cyclohexene. Under optimized reaction conditions, the oxidation of styrene gave 95% conversion where styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde are products. Oxidation of cyclohexene gave 96% conversion with cyclohexene oxide, 2-cyclohexene-1-ol, cyclohexane-1,2-diol and 2-cyclohexene-1-one as the major products. Neat complex K[V^VO₂(sal-iah)]·H ₂O (2) is equally active but the recyclability and heterogeneity tests of polymer-grafted complex make it better over neat analog.

Full text of DOI:10.1016/j.molcata.2013.12.006

Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Chloromethylated polystyrene cross-linked with divinylbenzene and
grafted with vanadium(IV) and vanadium(V) complexes having ONO
donor ligand for the catalytic activity
Mannar R. Maurya∗, Naveen Kumar
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 October 2013
Received in revised form 7 December 2013
Accepted 9 December 2013
Available online 17 December 2013
The ligand H2sal-iah (I), derived from salicylaldehyde and indole-3-acetic hydrazide, reacts with
[VIVO(acac)2] in methanol to give oxidovanadium(IV) complex [VIVO(sal-iah)(H2O)] (1). In the pres-
ence of KOH, arial oxidation of 1 in methanol yields dioxidovanadium(V) complex K[VVO2(sal-iah)]·H2O
(2). Complex 1 has been grafted via covalent bonding through imino nitrogen of the indole group to
chloromethylated polystyrene cross-linked with 5% divinylbenzene {now abbreviated as PS-[VIVO(sal-
iah)(H2O)] (3)}. Its oxidomethoxido vanadium(V) analog {PS-[VVO(OMe)(sal-iah)] (4)} can be obtained by
aerial oxidation of methanolic suspension of 3. All these complexes are characterized by various spectro-
scopic techniques (IR, electronic, 1H and 51V NMR, electron paramagnetic resonance (EPR) and thermal as
well as field-emission scanning electron micrographs (FE-SEM)) studies. The EPR spectrum of 3 indicates
that the magnetically dilute VIVO-centers are well dispersed in the polymer matrix while EPR spectrum
of 1 shows slightly different binding mode around vanadium center. 1H and 51V NMR spectra of 2 are
compatible with the existence of expected dioxide species as the major product and oxidomethoxido
species as a minor component in solution. Independent of the species presents in methanol, complexes
1 and 2 upon treatment with H2O2 both change to same oxidoperoxido species. The polymer-grafted
complex 4 catalyzes the oxidation, by H2O2, of styrene and cyclohexene. Under optimized reaction con-
ditions, the oxidation of styrene gave 95% conversion where styrene oxide, benzaldehyde, benzoic acid,
1-phenylethane-1,2-diol and phenylacetaldehyde are products. Oxidation of cyclohexene gave 96% con-
version with cyclohexene oxide, 2-cyclohexene-1-ol, cyclohexane-1,2-diol and 2-cyclohexene-1-one as
the major products. Neat complex K[VVO2(sal-iah)]·H2O (2) is equally active but the recyclability and
heterogeneity tests of polymer-grafted complex make it better over neat analog.
Keywords:
Polymer-grafted complexes
Oxidovanadium(IV) complex
Dioxidovanadium(V) complex
Oxidation of styrene
Oxidation of cyclohexene
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
cross-linked with divinyl benzene (PS-CH2Cl) as a solid support to
immobilize vanadium complexes and explore their catalytic poten-
The immobilization of catalysts on solid support has attracted
attention of researchers because this allows the design of ther-
mally more stable catalysts and environment-friendly synthetic
routes to fine chemicals. This way expensive homogeneous cata-
lyst also become separable from the reaction mixture by simple
filtration and meets the industrial demand of recyclability which
in turn improves the efficiency of the catalyst [1–4]. Several strate-
gies have been put forward on immobilization of homogeneous
catalysts. Even review articles highlight some of these methods
and explore the catalytic activities of such immobilized metal
complexes [5–9]. Our effort using chloromethylated polystyrene
tial for organic transformations offer some real prospects for the
development of more environmentally benign synthetic routes to
fine chemicals leading to technological applications [7,8]. In con-
tinuation of our efforts on the development of vanadium based
polymer-grafted catalysts [7,8], we report herein polymer-grafted
oxidovanadium(IV) and oxidomethoxido vanadium(V) complexes
of the indole-derived ONO donor ligand PS-H2sal-iah (I, Scheme 1)
for the oxidation of styrene and cyclohexene. Additional methylene
group attached to hydrazone moiety in combination with covalent
bonding through ring nitrogen of indole will act as spacer and hence
would enhance the availability of grafted complexes on the surface
of the polymer which may allow better interaction of substrates
and oxidant with metal center during catalytic reaction. The cor-
responding non polymer-grafted vanadium complexes have also
been prepared for comparison of their catalytic performance.
∗
Corresponding author. Tel.: +91 1332 285327; fax: +91 1332 273560.
E-mail address: rkmanfcy@iitr.ac.in (M.R. Maurya).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.12.006

M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
173
O
OH2
O
O
HO
O
V
N
C
C
MeOH
N
+ [VO(acac)2]
N
C
N
C
H
Reflux 6 h
H
H
N
H
N
H
H2sal-iah (I)
[VO(sal-iah)(H2O)] (1)
MeOH
1 eq. KOH
aerial oxidation
_
O
O
O
O
V
C
N
+
H2O
K
N
C
H
N
H
K[VO2(sal-iah)].H2O (2)
Scheme 1. Synthetic routes to prepare complexes 1 and 2.
2. Experimental
from thermal damage by the electron beam and to make the sam-
ple conductive. A Shimadzu 2010 plus gas-chromatograph fitted
with a Rtx-1 capillary column (30 m × 0.25 mm × 0.25 ␮m) and a
FID detector was used to analyze the reaction products and their
quantifications were made on the basis of the relative peak area of
the respective product. The identity of the products was confirmed
using a GC–MS Perkin-Elmer, model Clarus 500 and comparing the
fragments of each product with the library available. For more than
one cycle of catalytic experiment, the experiment was a bit difficult
as catalyst amount taken in original experiment was too less and
samples recovered from two such experiments were taken together
for first recycle study.
2.1. Materials
Chloromethylated polystyrene [18.9% Cl (5.35 mmol Cl per gram
of resin)] cross-linked with 5% divinylbenzene was obtained from
Thermax Limited, Pune, India. Analytical reagent grade V2O5, salic-
ylaldehyde, cyclohexene (Sisco, India), indole-3-acetic hydrazide,
styrene (Aldrich, USA) and 30% aqueous H2O2 (Rankem, India)
were used as obtained. [VIVO(acac)2] was prepared according to
the method reported in the literature [10]. Other chemicals and sol-
vents of analytical reagent grades were used without purifications.
2.3. Synthesis
2.2. Physical methods and analysis
2.3.1. H2sal-iah (I)
Elemental analyses of the complexes were obtained with an Ele-
mentar model Vario-EL-III. Vanadium content in polymer-grafted
complexes was obtained by inductively coupled plasma spectrom-
etry (ICP; Labtam 8440 plasma lab). Thermogravimetric analyses of
the complexes were carried out using Perkin Elmer (Pyris Diamond)
having weight sensitivity of 0.2 ␮g under oxygen atmosphere.
IR spectra were recorded (16 scans) as KBr pellets on a Nico-
let NEXUS Aligent 1100 FT-IR spectrometer having a resolution
of 4 cm−1. UV–visible spectra of the polymer-grafted complexes
were recorded with a medium scan speed in Nujol on a Shi-
madzu 1601 UV–Vis spectrophotometer having 0.1 nm wavelength
accuracy by layering a mull of the sample on the inside of one
of the cuvettes while keeping the other one layered with Nujol
as reference. Using BaSO4 as a background, electronic spectra of
the polymer-grafted complexes were also recorded after diluting
sample with BaSO4. Spectra of non-polymer-grafted ligands and
complexes were recorded in methanol. 1H NMR spectra (using
Bruker Avance III 500 MHz spectrometer) and 51V NMR spectra
(using Bruker Avance III 400 MHz spectrometer) with the com-
mon parameter settings were recorded with samples dissolved in
DMSO-d6, and the ı (51V) values are referenced relative to neat
VVOCl3 as external standard. EPR spectra were recorded with a
Bruker ESP 300E X-band spectrometer and the spin Hamiltonian
parameters were obtained by simulation of the spectra with the
computer program of Rockenbauer and Korecz [11]. The energy dis-
persive X-ray analyses (EDX) of anchored complexes were recorded
on a FEI Quanta 200 FEG. The samples were coated with a thin film
of gold to prevent surface charging, to protect the surface material
A mixture of indole-3-acetic hydrazide (1.89 g, 10 mmol) and
salicylaldehyde (1.22 g, 10 mmol) in 100 mL of methanol was
stirred for 2 h. A white solid precipitated during this period was fil-
tered off, washed with methanol and dried. Recrystallization from
methanol yielded pure I as a white solid. Yield 2.5 g (85%). Anal.
Calc. for C17H15N3O2 (293.33): C, 69.61; H, 5.15; N, 14.33. Found:
C, 69.7; H, 5.2; N, 13.9%.
2.3.2. [VIVO(sal-iah)(H2O)] (1)
A hot solution of H2sal-iah (2.93 g, 10 mmol) in methanol
(150 mL) was treated with [VIVO(acac)2] (2.65 g, 10 mmol) in one
portion and the resulting mixture was heated under reflux for 6 h.
After reducing the solvent volume to 20 mL and standing the solu-
tion under sealed flask for 24 h, the dark brown solid precipitated.
This was filtered, washed with methanol and dried in vacuo. Yield
2.1 g (55.8%). Anal. Calc. for C17H15N3O4V (376.27): C, 54.27; H,
4.02; N, 11.17. Found: C, 54.4; H, 4.1; N, 11.3%.
2.3.3. K[VVO2(sal-iah)]·H2O (2)
Complex 1 (0.376 g, 1 mmol) was dissolved in methanol (40 mL)
having KOH (0.056 g, 1 mmol) and air was slowly passed through
the solution with occasional shaking while maintaining the solvent
volume to 40 mL. After 2 days the dark brown solution gradu-
ally changed to light brown. After reducing the solvent to ca.
20 mL the flask was kept at ambient temperature for overnight
where light brown solid precipitated. This was filtered off, washed
with methanol and dried. Yield 0.23 g (55.7%). Anal. Calc. for

174
M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
O
OH2
O
O
O
OH2
O
O
V
N
DMF, 80 oC
V
N
C
C
N
C
Triethylamine,
Ethyleacetate
N
N
Cl
H
C
N
H
H
Chloromethylated polystyrene
[PS]
[VO(sal-iah)(H2O)] (1)
PS-[VO(sal-iah)(H2O)](3)
KOH
MeOH
Pass air for 4 days
O
OMe
O
O
V
C
N
N
C
H
N
PS-[VO(OMe)(sal-iah)] (4)
Scheme 2. Synthetic routes to prepare PS-[VIVO(sal-iah)(H2O)] (3) and PS-[VVO(OMe)(sal-iah)] (4); PS (or ball) represents the backbone of the chloromethylated polystyrene.
C17H15N3O5KV (431.36): C, 47.34; H, 3.50; N, 9.74. Found: C, 48.9;
H, 3.8; N, 9.4%.
while stirring in an oil bath. After removing the catalyst by filtration,
the reaction products were analyzed as mentioned above.
2.3.4. PS-[VIVO(sal-iah)(H2O)] (3)
3. Results and discussion
Chloromethylated polystyrene (3.0 g) was allowed to swell in
DMF (20 mL) for 2 h. A solution of [VIVO(sal-iah)(H2O)] (3.0 g,
7.98 mmol) in DMF (20 mL) was added to the above suspension
followed by triethylamine (4.0 g) in ethylacetate (20 mL), and the
obtained reaction mixture was heated at 80 ◦C for 24 h with con-
tinuous but slow stirring. After cooling to room temperature, the
polymer-grafted complex was separated by filtration, washed with
hot DMF, followed by hot methanol and dried in an oven in air at
110 ◦C.
3.1. Synthesis and characterization
Reaction between equimolar amounts of indole-3-acetic
hydrazide and salicylaldehyde in refluxing methanol gave ligand
H2sal-iah (I). The ligand I reacts with [VIVO(acac)2] in MeOH to give
[VIVO(sal-iah)(H2O)] (1). Complex K[VVO2(sal-iah)]·H2O (2) can be
isolated by aerial oxidation of 1 in the presence of one equivalent of
KOH in methanol (Scheme 1). Elemental analyses and spectroscopic
(IR, UV–vis, EPR, 1H and 51V NMR) studies of ligand and complexes
are in agreement with the proposed structures.
2.3.5. PS-[VVO(OMe)(sal-iah)] (4)
Air was slowly passed through the methanolic (100 mL) suspen-
sion of PS-[VIVO(sal-iah)(H2O)] (3) in the presence of KOH (0.3 g,
5.35 mmol) for ca. 4 days. The light brown beads were filtered off,
washed with hot methanol and dried in an oven in air at 110 ◦C.
The reaction of chloromethylated polystyrene (cross linked with
5% divinylbenzene) with oxidovanadium(IV) complex 1 in DMF
at 80 ◦C in the presence of triethylamine leads to the formation
of polymer-anchored complex PS-[VIVO(sal-iah)(H2O)] (3). Dur-
ing this process, the labile proton of NH group of indole reacts
with CH2Cl group of polymer. Complex 3 on aerial oxidation in
methanol in the presence of KOH gave the oxidomethoxido vana-
dium(V) complex, PS-[VVO(OMe)(sal-iah)] (4). Upon contact of 4
with dimethyl sulfoxide (DMSO) for 15 h, the GC–MS detected the
presence of MeOH in solution confirming the presence of MeO− in
the complex.
2.4. Catalytic activity
The catalytic oxidation of styrene and cyclohexene was car-
ried out in a 50 mL flask fitted with a water circulated condenser.
Polymer-grafted catalysts were kept in CH3CN for 1 h before use.
The whole synthetic procedures are presented in Scheme 2. The
ICP-MS analysis of vanadium in the polymer-grafted complexes
suggest vanadium loading of 0.36 and 0.23 mmol g−1 of polymer
resin in 3 and 4, respectively.
2.4.1. Oxidation of styrene
In a typical reaction, an aqueous solution of 30% H2O2 (3.40 g,
30 mmol) and styrene (1.04 g, 10 mmol) were mixed in 5 mL of
CH3CN and the reaction mixture was heated at 80 ◦C with con-
tinuous stirring in an oil bath. The reaction was considered to
begin after addition of 0.020 g (polymer-grafted) or 1.898 × 10−3 g
of (non-polymer-grafted) catalyst. During the reaction, the reaction
products were analyzed using a gas chromatograph by withdraw-
ing small aliquots after specific interval of time and confirming their
identity by GC–MS.
3.2. Field emission-scanning electron micrograph (FE-SEM) and
energy dispersive X-ray analysis (EDX) studies
Single beads of pure chloromethylated polystyrene and
polymer-grafted complex PS-[VVO(OMe)(sal-iah)] (4) were
selected to record field emission-scanning electron micrographs
(Fe-SEM) in order to understand the morphological changes.
Representative image of each one is reproduced in Fig. 1. The pure
chloromethylated polystyrene bead has smooth and flat surface
while anchored complex shows slight roughening of the top layer.
Accurate information on the morphological changes in terms of
2.4.2. Oxidation of cyclohexene
An aqueous solution of 30% H2O2 (1.135 g, 10 mmol), cyclo-
hexene (0.82 g, 10 mmol) and 0.010 g (polymer-grafted) or
0.949 × 10−3 g of (non-polymer-grafted) catalyst were mixed in
5 mL of CH3CN and the reaction mixture was heated at 80 ◦C for 3 h

M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
175
Fig. 1. Scanning electron micrographs (SEM) of chloromethylated polystyrene (left) and PS-[VVO(OMe)(sal-iah)] (4) (right).
exact orientation of ligand coordinated to the metal ion has not
been possible due to poor loading of the metal complex. However,
energy dispersive X-ray analysis (EDX) of PS-[VVO(OMe)(sal-iah)]
(4) estimates ca. 2.4 weight percentage of vanadium content.
This observation confirms the grafting of metal complex onto
polystyrene beads and part of the covalently bonded complexes is
present on the surface while remaining at various sites.
indicative of its ketonic nature in the solid state. The absence of
later band in the spectra of all complexes is consistent with the
enolization of the amide functionality and subsequent coordina-
tion of enolic oxygen to the metal ion after proton replacement.
A new band appearing in the region 1280 cm−1 is assigned to
the ␯(C O)(enolic) stretching of the coordinated hydrazone frag-
ment. The band at 3400 cm−1 corresponds to the free OH group
present in H2sal-iah ligand. However, the presence of this band
in complexes 1–3 may possibly be due the presence of coordi-
nated/residual water. The chloromethylated polystyrene shows
strong peaks at 1264 and 673 cm−1 [15] and the absence of these
peaks in PS-[VVO(OMe)(sal-iah)] (4) suggests the covalent bond-
ing of chloromethylated polystyrene with K[VVO2(sal-iah)]·H2O
(cf. Scheme 2) through nitrogen of the benzimidazole ring. This
is further supported by the absence of ␯(NH) band appearing at
3054 cm−1 in K[VVO2(sal-iah)]·H2O. The presence of multiple bands
of medium intensity covering the 2800–2900 cm−1 regions sug-
gests the existence of CH2 group.
3.3. Thermogravimetric study
Thermogravimetric analysis of polymer-grafted complexes car-
ried out under an oxygen atmosphere shows their good stability
up to ca. 180 ◦C except small weight loss between 100 and 190 ◦C
possibly due to loss of residual/coordinated water. Thereafter, they
decompose in three major fragments with exothermic weight loss
at higher temperature. Quantitative measurement of weight loss
and distinction between decomposition pattern of complex and
polymer matrix at various stages were not possible due to overlap-
ping nature of the decompositions. However, the final residues of
6.3% (equivalent to 0.35 mmol g−1 of resin in 3) and 5.0% (equivalent
to 0.28 mmol g−1 of resin in 4) at ca. 515 ◦C suggest the formation
of V2O5 and metal complexes are grafted into polymer support. A
representative plot is shown in Fig. S1 of supporting information.
The non polymer-grafted complex 1 exhibits a sharp band at
933 cm−1 due to ꢀ(V O) while 2 exhibits two such bands at 885
and 963 cm−1 corresponding to ꢀsym(O
V O) and ꢀasym(O V O)
modes, respectively. The corresponding polymer-bound vanadium
complexes display these bands at 900 cm−1 (in 3) and 906 cm−1 (in
4) [12,13].
3.4. IR spectral study
3.5. UV-visible spectral study
A partial list of IR spectral data of the ligand and the complexes
is presented in Table 1. A band appearing at 1618 cm−1 in H2sal-
iah (I) corresponds to azomethine group, and this band moves
toward lower wave number by 26 cm−1 (in 1) and 08 cm−1 (in 2)
indicating the coordination of azomethine nitrogen to the vana-
dium [12,13]. In the polymer-bound complexes this band appears at
1608 cm−1 (in 3) and 1610 cm−1 (in 4). The IR spectrum of the ligand
exhibits ␯(NH) and ␯(C O) at 3186 and 1670 cm−1, respectively
while DFT calculation on similar system suggests the assignment
of later band due to entire N(H)C( O) amide group [14]. These are
Table 2 includes UV–visible spectral data of the ligand and
complexes; Fig. 2 (A and B) presents spectra. Ligand H2sal-iah (I)
exhibits three spectral bands in the UV region corresponding to
␴→␴* (220 nm), ␲→␲* (279 nm) and n→␲* (321 nm) transitions.
The additional band at 289 nm is possibly due to splitting of ␲→␲*
transition. All these bands also appear in the spectra of complexes
1 and 2 with slight variations. They also exhibit a ligand to metal
charge transfer (LMCT) transition at ca. 400 nm from the phenolate
oxygen atom to an empty d-orbital of the vanadium atom [16,17].
Table 1
IR spectral data (cm−1) of compounds.
Compound
ꢁ(OH)
ꢁ(C O)
ꢁ(NH)
ꢁ(C N)
ꢁ(V O)
H2sal-iah (I)
3400
3350
3330
3420
1670
3186
3182
3054
1618
1592
1610
1608
1610
–
[VIVO(sal-iah)(H2O)] (1)
K[VVO2(sal-iah)]·H2O (2)
PS-[VIVO(sal-iah)(H2O)] (3)
PS-[VVO(OMe)(sal-iah)] (4)
933(s)
963, 885(s)a
900(s)
906
a
Bands correspond to asymmetric and symmetric (O
V
O) modes, respectively.

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M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
(A)
(B)
2.5
2.0
1.5
1.0
0.5
0.0
0.8
0.6
0.4
0.2
0.0
0.4
0.3
0.2
0.1
0.0
785 nm
(b)
(b)
(a)
(c)
700 800 900 1000 1100
(b)
(a)
250
300
400
500
600
700
800
200
300
350
400
450
500
Wavelength (nm)
Wavelength (nm)
Fig. 2. (A) UV–visible spectra of (a) H2sal-iah, (b) [VIVO(sal-iah)(H2O)] (1) and (c) K[VVO2(sal-iah)]·H2O (2) recorded in methanol. (B) UV–visible spectra of (a) PS-[VIVO(sal-
iah)(H2O)] (3) and (b) PS-[VVO(OMe)(sal-iah)] (4) recorded after dispersing them in Nujol®
.
calculated using the additivity relationship [Azest = ꢃAz,i (i = 1–4)]
proposed by Wüthrich [19] and Chasteen [20], with esti-
mated accuracy of 3 × 10−4 cm−1. Assuming the binding modes
(a)
(b)
involving (Owater, Ophenolate, Oenolate, Nimine,)equatorial, (Ooxido
)
,
axial
est
the Az
values have been calculated for 1 and 3 from
the partial contributions of the equatorial donor groups rel-
evant in the present case {H2O (45.7 × 10−4 cm−1), Ophenolate
(38.9 × 10−4 cm−1), Nimine (38.1–43.7 × 10−4 cm−1), O-enolate(−1)
(37.6 ×10−4 cm−1)}. The calculated value of 160.3 × 10−4cm−1
for PS-[VIVO(sal-iah)(H2O)] (3) is in good agreement with exper-
imental value (160.82 × 10−4 cm−1) while the calculated value
of 165.9 × 10−4 cm−1 for [VIVO(sal-iah)(H2O)] (1) slightly differs
with the experimental value of 174.11 × 10−4 cm−1, suggesting the
involvement of some other binding atom as well.
2.6
2.4
2.2
2
1.8
1.6
(g)
Fig. 3. 1st derivative EPR spectra of (a) PS-[VIVO(sal-iah)(H2O)] (3) at room tem-
perature and (b) [VIVO(sal-iah)(H2O)] (1) at frozen (77 K) solutions (ca. 4 mM) in
DMSO.
In addition, a new band at 785 nm in 1 is assigned due to d–d
transition [18]. As VV-complex 2 has 3d0 configuration, d–d band
is not expected. Complexes 3 and 4 have very similar electronic
spectral patterns (Fig. 2(B)) in the UV/visible region in Nujol®. In
addition to ␲→␲* (at ca. 300 nm) and n→␲* (at ca. 325 nm) tran-
sitions, a ligand to metal charge transfer (LMCT) transition at ca.
400 nm [12,14,16] has also been observed in these complexes. The
expected d–d transition in 3 could not be observed in Nujol pos-
sibly due to poor loading of complex in polymer matrix; however,
diffuse reflectance spectrum of PS-[VIVO(sal-iah)(H2O)] in BaSO4
exhibits a weak broad band at ca. 630 nm; Fig. S2.
3.7. 1H and 51V NMR studies
The 1H NMR spectrum of the ligand exhibits two sets of singlet
with about 1:2 ratio each for azomethine ( CH
N ), methylene
(
CH2 ) and NH (of C(O) NH group) protons and one signal
each for phenolic ( OH, singlet) and NH (doublet) protons of indole,
indicating its existence in the two isosmeric forms. In the com-
plex K[VVO2(sal-iah)]·H2O (2), absence of 11.17 ppm signal due to
the phenolic proton and shift of the azomethine signals from 8.38
and 8.41 ppm to 8.77 and 8.81 ppm indicates the coordination of
the phenolic oxygen after proton replacement and the azomethine
nitrogen. The signals at 3.66 and 4.02 ppm due to methyl protons
collapse into one and appear at 3.84 ppm while doublet at ca. 10.9
remains almost constant. Aromatic protons of ligand and complex
2 resonate at nearly same positions; however, complexity of sig-
nals in aromatic region does not allow separating their positions.
Thus, 1H NMR data suggests the formation of complex but the pres-
ence of two azomethine signals of about 2:3 ratio hints toward
the existence of two different vanadium(V) species (vide infra) in
solution.
3.6. EPR study
The EPR spectra of neat complex [VIVO(sal-iah)(H2O)] (1)
in “frozen” (77 K) DMSO solution and polymer-grafted com-
plex PS-[VIVO(sal-iah)(H2O)] (3) in DMSO at room temperature
are depicted in Fig. 3. The spectra were simulated and the
spin Hamiltonian parameters obtained by simulation of the
spectra are included in Table 3. The value of
A
can be
||
Table 2
UV–visible spectral data of ligand and complexes.
The 51V NMR spectrum of K[VVO2(sal-iah)]·H2O (2) shows
three resonances at ı = −534.3 ppm (72%), −567.3 ppm (22%) and
−467 ppm (6.1%); Fig. S3. The resonance at ı = −534.3 ppm (72%)
corresponds to proposed dioxido species and is in the range
reported for several dioxidovanadium(V) complexes containing a
mixed O/N donor set [12,13,21]. Other band at −567 ppm (21.9%) is
probably due to methoxido complex [VVO(OMe)(MeOH)(sal-iah)].
Compound
Solvent
ꢂmax/nm
H2sal-iah (I)
MeOH
MeOH
MeOH
Nujol
Nujol
220, 279, 289, 321
[VIVO(sal-iah)(H2O)] (1)
K[VVO2(sal-iah)]·H2O (2)
PS-[VIVO(sal-iah)(H2O)] (3)
PS-[VVO(OMe)(sal-iah)] (4)
211, 271, 286, 312, 398, 785
220, 270, 289, 312, 400
300, 325, 405
292, 322, 402
Table 3
Spin Hamiltonian parameters obtained by simulation of the experimental 1st derivative EPR spectra.
Complexes
g
||
A
||
(×10−4 cm−1
)
g
⊥
A
(×10−4 cm−1
⊥
)
[VIVO(sal-iah)(H2O)] (1)
1.942
1.949
174.11
160.82
1.979
1.983
63.96
57.79
PS-[VIVO(sal-iah)(H2O)] (3)

M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
177
Such methoxido complexes are known to form upon keeping cor-
O
responding dioxidovandium(V) species in methanol for prolonged
period of time [12,14]. These observations supplement the data
obtained from 1H NMR study. Interpretation of minor species show-
ing signal at ı = −467 ppm (6%) remains elusive.
Phenylacetaldehyde
(phaa)
O
HO
OH
Catalyst
H2O2
3.8. Catalytic activity studies
1-phenylethane-1,2-diol
(phed)
Styreneoxide
(s o)
Styrene
3.8.1. Oxidation of styrene
Oxidation of styrene has been reported using homogeneous
as well as heterogeneous catalysts [22–26]. Amongst the vari-
ous oxidation products of styrene, styrene oxide is an important
intermediate in organic synthesis and in the manufacture of the
perfumery chemical, phenyl ethyl alcohol. Using 30% aqueous H2O2
as an oxidant, the oxidation of styrene was carried out taking
PS-[VVO(OMe)(sal-iah)] (4) as catalyst and five oxidation prod-
ucts namely styreneoxide, benzaldehyde, 1-phenylethane-1,2-diol,
benzoic acid and phenyl acetaldehyde were obtained along with
small amount of unidentified product (Scheme 3).
O
HO
O
Benzoic acid
(bzac)
Benzaldehyde
(bza)
Scheme 3. Oxidation products of styrene using PS-[VVO(OMe)(sal-iah)] (4) as cat-
alyst.
With the objective to achieve suitable reaction conditions for
the maximum oxidation of styrene different parameters, namely,
the amount of oxidant (mol of H2O2 per mol of styrene), catalyst
(amount of catalyst per mole of styrene), solvent and temperature
of the reaction mixture were tested.
For three different amounts (i.e. 0.015, 0.020 and 0.025 g) of
catalyst, the fixed amount of styrene (1.04 g, 10 mmol) and H2O2
(3.40 g, 30 mmol) were taken in 5 mL of CH3CN and the reaction
was carried out at 80 ◦C. The formation of products was regularly
analyzed at definite time intervals. As illustrated in Fig. 4(a), the
conversion increases on increasing the amount of catalyst from
0.015 g to 0.020 g and a maximum of 95% conversion was achieved
with 0.020 g of catalyst. The oxidation improved only marginally
upon further increasing the amount of catalyst to 0.025 g. Therefore,
an amount of 0.020 g catalyst may be considered as optimum to
obtain the maximum conversion of styrene.
To study the effect of oxidant, three different styrene: aque-
ous 30% H2O2 molar ratios viz. 1:1, 1:2, and 1:3 were considered
while taking the amount of styrene (1.04 g, 10 mmol) and catalyst
(0.020 g) in 5 mL of CH3CN and the reaction was carried out at 80 ◦C.
As illustrated in Fig. 4(b), increasing the styrene to oxidant ratio
from 1:1 to 1:2 improved the conversion from 69 to 89%. A maxi-
mum of 95% conversion of styrene was obtained on increasing this
ratio to 1: 3. However, further increasing the ratio, no predominant
conversion took place. The reason for this may be due to the dilution
of the reaction mixture by the presence of larger amount of water
molecules in H2O2 solution. Therefore, styrene to H2O2 molar ratio
of 1:3 was taken for further optimization of other parameters.
Fig. 4. (a) Effect of the amount of catalyst PS-[VVO(OMe)(sal-iah)] (4) on the oxidation of styrene. Reaction conditions: styrene (1.04 g, 10 mmol), 30% H2O2 (3.40 g, 30 mmol),
CH3CN (5 mL) and reaction temp. (80 ◦C). (b) Effect of volume of H2O2 amount (H2O2/styrene molar ratio) on the oxidation of styrene. Reaction conditions: styrene (1.04 g,
10 mmol), catalyst (0.020 g), CH3CN (5 mL) and reaction temp. (80 ◦C). (c) Effect of temperature on the oxidation of styrene. Reaction conditions: styrene (1.04 g, 10 mmol),
catalyst (0.020 g), 30% H2O2 (3.40 g, 30 mmol) and CH3CN (5 mL). (d) Effect of solvent (acetonitrile) volume on the oxidation of styrene. Reaction conditions: styrene (1.04 g,
10 mmol), catalyst (0.020 g), 30% H2O2 (3.40 g, 30 mmol) and reaction temp. (80 ◦C).

178
M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
Table 4
Percent conversion for 10 mmol of styrene under different reaction conditions using PS-[VVO(OMe)(sal-iah)] (4) as catalyst and products selectivity of products after 6 h of
reaction time.
Entry no.
Catalyst (g)
Temp. (◦C)
H2O2 (g, mmol)
CH3CN (mL)
% Conv., TOF
% Selectivitya
so
bza
phed
bzac
phaa
Others
1.
2
3
4
5
6
7
8
9
0.015
0.020
0.025
0.020
0.020
0.020
0.020
0.020
0.020
80
80
80
60
70
80
80
80
80
3.40, 30
3.40, 30
3.40, 30
3.40, 30
3.40, 30
1.135, 10
2.27, 20
3.40, 30
3.40, 30
5
5
5
5
5
5
5
10
15
80, 387
95, 344
97, 282
69, 250
86, 312
69, 250
89, 327
64, 232
46, 167
3.5
3.3
4.2
4.1
4.6
5.0
3.0
2.2
1.8
63.6
66.9
73.4
87.8
75.0
50.4
56.7
67.7
55.1
11.6
4.5
4.1
0.0
3.4
20.9
16.5
4.5
9.0
16.6
11.1
4.1
7.3
8.8
8.5
10.1
5.9
2.9
5.2
5.5
4.0
5.9
6.0
3.8
3.8
3.7
9.4
3.5
1.7
0.00
3.8
8.9
11.5
11.7
11.2
22.3
a
so, styrene oxide; bza, benzaldehyde; phed, 1-phenylethane-1,2-diol; bzac, benzoic acid; phaa, phenyl acetaldehyde.
Under above optimized reaction conditions, temperature of the
reaction mixture was also optimized and found that 80 ◦C (Fig. 4(c))
is the most suitable one to obtained highest conversion. Similarly,
5 mL of acetonitrile was found to be the most suitable one to obtain
a maximum of 95% conversion of styrene in 6 h of reaction time
(Fig. 4 (d)). Table 4 provides conversion of styrene under different
reaction conditions and selectivity of different reaction products
under particular condition after 6 h of reaction time. From the data
presented in table, it is clear that the best suited reaction condi-
tions (entry no. 2, Table 4) for the maximum oxidation of 10 mmol
of styrene are: PS-[VVO(OMe)(sal-iah)] (4) (0.020 g), aqueous 30%
H2O2 (3.40 g, 30 mmol), CH3CN (5 mL) and reaction temperature
(80 ◦C).
The conversion of styrene and the selectivity of different reac-
tion products using PS-[VVO(OMe)(sal-iah)] (4) as catalyst under
the optimized reaction conditions have been analyzed as a func-
tion of time and are presented in Fig. 5. It is clear from the plot
that the selectivity of the formation of benzaldehyde is good in the
beginning but decreases slowly with time and reaches 66.9% at the
end of 6 h. The selectivity of the formation of all other products is
much low and falls between 3 and 17%. Thus, with the maximum
styrene oxidation of 95% at the end of 6 h under optimized reaction
conditions, the selectivity of different products follows the order:
benzaldehyde (66.9%) > benzoic acid (16.6%) > phenyl acetaldehyde
(5.2%) > 1-phenylethane-1,2-diol (4.5%) > styrene oxide (3.3%).
The formation of benzaldehyde is generally considered to
proceed by the direct oxidative cleavage of the styrene side chain
double bond by a radical mechanism [23,24]. A nucleophilic attack
of H2O2 on styrene oxide followed by cleavage of the interme-
diate hydroperoxystyrene also provides benzaldehyde [27]. The
oxidation of benzaldehyde provides benzoic acid while the for-
mation of other products such as phenylacetaldehyde is possible
through isomerization of styrene oxide.
The recycled catalyst showed slightly less conversion (93%)
compared to fresh one. Under the above reaction conditions
catalytic activity of non-polymer-grafted complex K[VVO2(sal-
iah)]·H2O gave 90% conversion with essentially same order of
the selectivity of reaction products (Fig. 6). Thus, polymer-grafted
complex is better catalyst over neat complex. Further, the recycla-
bility of the polymer-grafted catalyst makes it better over the non
polymer-grafted one. The literature contains very limited reports
on the polymer-grafted vanadium based catalysts for the oxidation
of styrene [24–29]. However, the catalytic activity of polymer-
grafted catalyst reported here compares well with the catalytic
activity reported in the literature. For example, PS-K[VVO2(sal-
ohyba)] (H2sal-ohyba = Schiff base derived from 3-formylsalicylic
acid and o-hydroxybenzylamine) exhibited as high as 73%
conversion [25a] while PS-[VIVO(hmbmz)2] gave only 48% con-
version [29]. Other polymer-grafted oxidovanadium(IV) complexes
PS-[VIVO(fsal-ea)·DMF], PS-[VIVO(fsal-pa)·DMF] and PS-[VIVO(fsal-
amp)·DMF] (where H2fsal-ea/pa/amp = Schiff bases derived from
3-formylsalicylic acid and 2-aminoethanol/3-aminopropanol/2-
amino-2-methylpropanol) showed 82–95% conversion [26]. In the
absence of catalyst, the reaction mixture gave only 15% conversion
of styrene under above optimized reaction conditions.
3.8.2. Oxidation of cyclohexene
Cyclohexene epoxide, an oxidation product of cyclohex-
ene, is
a highly reactive and selective organic intermedi-
ate widely used in the synthesis of enantioselective drugs,
epoxy paints and rubber promoters. Oxidation of cyclohexene
100
80
60
40
20
0
0
20
100
PS-[VO(OMe)(sal-iah)]
(a)
K[VO (Sal-iah)]H O
Without catalyst
80
(b)
40
Styrene
Benzaldehyde
Styrene oxide
Phenyl acetaldehyde
Benzoic acid
60
60
1-Phenyl ethane- 1,2-diol
others
40
80
(c)
20
100
60
120
180
240
300
360
0
Time (min.)
0
60
120
180
240
300
360
Time (min.)
Fig. 5. Consumption of styrene and variation in the selectivity of different reac-
tion products as a function of time. Reaction conditions: styrene (1.04 g, 10 mmol),
catalyst (0.020 g), 30% H2O2 (3.40 g, 30 mmol), CH3CN (5 mL) and reaction temp.
(80 ◦C).
Fig. 6. Conversion of styrene with time: (a) PS-[VVO(OMe)(sal-iah)] (4), (b)
K[VVO2(sal-iah)]·H2O (2) and (c) without catalyst.

M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
179
(b)
(a)
100
80
60
40
20
0
100
80
60
40
20
0
1:3
1:2
1:1
0.020 g
0.015 g
0.010 g
0
30
60
90
120
150
180
0
30
60
90
120
150
180
Time/min
Time/min
100
80
60
40
20
0
100
80
60
40
20
0
(c)
(d)
15 mL
10 mL
5 mL
80 0C
70 0C
60 0C
0
30
60
90
120
150
180
0
30
60
90
120
150
180
Time/min
Time/ min
Fig. 7. (a) Effect of the amount of catalyst {PS-[VVO(OMe)(sal-iah)] (4)} on the oxidation of cyclohexene. Reaction conditions: cyclohexene (0.82 g, 10 mmol), 30% H2O2
(1.135 g, 10 mmol), CH3CN (10 mL) and reaction temp. (80 ◦C). (b) Effect of amount of H2O2 (H2O2/styrene molar ratio) on oxidation of cyclohexene. Reaction conditions:
cyclohexene (0.82 g, 10 mmol), catalyst (0.010 g), CH3CN (10 mL) and reaction temp. (80 ◦C). (c) Effect of volume of solvent (acetonitrile) on the oxidation of cyclohexene.
Reaction conditions: cyclohexene (0.82 g, 10 mmol), catalyst (0.010 g), 30% aqueous H2O2 (1.135 g, 10 mmol) and reaction temp. (80 ◦C). (d) Effect of temperature on the
oxidation of cyclohexene. Reaction conditions: cyclohexene (0.82 g, 10 mmol), catalyst (0.010 g), 30% aqueous H2O2 (1.135 g, 10 mmol) and CH3CN (5 mL).
OH
varying the amount of catalyst (0.010, 0.015 and 0.020 g), 30%
aqueous H2O2 (10, 20 and 30 mmol), temperature of the reac-
tion mixture (60, 70 and 80 ◦C) and volume of acetonitrile (5,
10 and 15 mL). About 3 h was required to attain the equilib-
rium. Fig. 7 provides plots for the conversion of cyclohexene at
various reaction conditions as a function of time and Table 5
summarizes all conditions and conversion obtained under partic-
ular condition. From the data in the table and plots shown, the
best suited reaction conditions concluded for the catalytic activity
of PS-[VVO(OMe)(sal-iah)] (4) for the maximum oxidation (96%)
of 10 mmol (0.82 g) of cyclohexene are: catalyst (0.010 g), 30%
aqueous H2O2 (1.135 g, 10 mmol), CH3CN (5 mL) and reaction tem-
perature (80 ◦C). Under these conditions (entry no. 6, Table 5)
the selectivity of different reaction products are: cyclohexene
epoxide (39.3%) > 2-cyclohexene-1-ol (23.9%) > cyclohexane-1,2-
diol (22.9%) > 2-cyclohexene-1-one (7.9%). The preferential attack
+
O
OH
cyclohexene oxide
cyclohexane-1,2-diol
O
OH
cyclohexene
+
2-cyclohexene-1-ol
2-cyclohexene-1-one
Scheme 4. Various oxidation products of cyclohexene.
catalyzed by PS-[VVO(OMe)(sal-iah)] (4) gave cyclohexene epoxide,
2-cyclohexene-1-ol, cyclohexane-1,2-diol and 2-cyclohexene-1-
one as presented in Scheme 4. For this catalytic reaction, conditions
were also optimized using 10 mmol (0.82 g) of cyclohexene,
of the activated
C H bond over the C C bond favors the
Table 5
Percent conversion of 10 mmol (0.82 g) of cyclohexene using PS-[VVO(OMe)(sal-iah)] (4) as catalyst after 3 h of reaction time and selectivity of products.
Entry no.
Catalyst (g)
Temp. (◦C)
H2O2 (g, mmol)
CH3CN (mL)
% Conv., TOF
% Selectivity
OH
O
OH
OH
O
Other
1.
2
3
4
5
6
7
8
9
0.010
0.015
0.020
0.010
0.010
0.010
0.010
0.010
0.010
80
80
80
80
80
80
80
60
70
2.27, 20
2.27, 20
2.27, 20
1.135, 10
3.40, 30
1.135, 10
1.135, 10
1.135, 10
1.135, 10
10
95, 1379
97, 939
98, 711
97, 1408
97, 1408
96, 1393
91, 1321
82, 1190
83, 1205
32.6
36.5
39.7
39.1
26.6
39.3
33.8
39.2
35.6
37.5
23.9
29.2
30.1
44.1
23.9
32.4
30.8
41.7
5.6
10.7
7.2
5.8
5.6
7.9
6.5
8.4
5.1
18.5
17.3
15.8
20.4
16.7
22.9
21.4
15.6
15.5
5.8
11.6
8.1
4.6
7.0
6.0
5.9
6.0
2.1
10
10
10
10
5
15
5
5

180
M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
100
80
60
40
20
0
0
20
100
80
60
40
20
0
PS-[VO(OMe)(sal-iah)]
K[VO (sal-iah)]H O
Without Catalyst
(a)
(b)
Cyclohexene
2-Cyclohexene 1-ol
Cyclohexene oxide
2-Cyclohexene i-one
1,2- Diol
40
Others
60
80
(c)
100
30
60
90
120
150
180
Time (min.)
0
30
60
90
120
150
180
Time (min.)
Fig. 8. Consumption of cyclohexene and variation in the selectivity of different
reaction products as a function of time. Reaction conditions: cyclohexene (0.82 g,
10 mmol), catalyst (0.010 g), 30% H2O2 (1.135 g, 10 mmol), CH3CN (5 mL) and reac-
tion temp. (80 ◦C).
Fig. 9. % Conversion of cyclohexene with time (a) PS-[VVO(OMe)(sal-iah)] (4), (b)
K[VO2(sal-iah)]H2O, and (c) without catalyst.
oxidovanadium(IV) complex immobilized on chloromethylated
polystyrene [34].
formation of allylic oxidation products 2-cyclohexene-1-one and
2-cyclohexene-1-ol while epoxidation occurs via the direct reac-
tion of the olefin with the coordinated peroxido group to vanadium
[30]. The species responsible for the cyclohexene oxidation is the
product formed from the cleavage of the O O bond [31].
3.9. Reactivity of K[VVO2(sal-iah)]·H2O with H2O2 and possible
reaction pathway of the catalyst
The consumption of cyclohexene and the selectivity of dif-
ferent products under the optimized reaction conditions have
also been analyzed as a function of time and are presented in
Fig. 8. The selectivity of cyclohexene oxide and 2-cyclohexene-
1-one remains nearly constant with time during reaction while
that of 2-cyclohexene-1-ol decreases from 45% at 1/2 h to 23.9%
after 3 h and cyclohexane-1,2-diol increases from 5% to 22.9%. The
catalytic activity of recycled catalyst shows slightly less (92%) con-
version. Under the above reaction conditions the catalytic activity
of non-polymer-grafted complex K[VVO2(sal-iah)]·H2O gave 90%
conversion with essentially similar selectivity of reaction products.
Control experiment without catalyst under above reaction condi-
tions gave only 20% conversion (Fig. 9).
Polymer-grafted vanadium complex reported here shows better
conversion than polymer-grafted vanadium complexes reported
in the literature [8]. Amino acids based polymer-grafted oxi-
dovavandium(IV) complexes show as high as 79% conversion of
cyclohexene with ca. 39% selectivity of cyclohexene oxide and ca.
50% of 2-cyclohexene-1-ol [32,33]. A maximum of 86% conver-
sion of cyclohexene with major product of cyclohexane-1,2-diol
(81% selectivity) and only minor product of cyclohexene oxide
(3% selectivity) was noted by thiomethylbenzimidazole based
The oxidoperoxidovanadium(V) complex [VVO(O2)(sal-iah)],
one of the important intermediate form during catalytic reac-
tion, could not be isolated in the solid state by the reaction of
K[VVO2(sal-iah)]·H2O (2) and H2O2 due to its instability at ambient
temperature. However, its formation has been established in solu-
tion by electronic absorption spectroscopy. The observed spectral
changes are depicted in Fig. 10. Thus, the titration of a methano-
lic solution of K[VVO2(sal-iah)]·H2O (4.0 × 10−5 M) with 30% H2O2
(two drops) dissolved in 5 mL of MeOH results in the shift of 400 nm
band to 390 nm along with slight increase in intensity; Fig. 10(a).
The band at 312 nm remains nearly unchanged with partial reduc-
tion in intensity. Such changes in the UV/vis spectra have been
interpreted as involving the progressive conversion of dioxido com-
plex into oxidoperoxido species [12,13]. The d–d band appearing
at 785 nm recorded with a concentrated solution (2.4 × 10−2 M) of
[VIVO(sal-iah)(H2O)] (1) in DMSO slowly decreases the intensity
and finally becomes indistinguishable; Fig. 10(b). Effect of H2O2
on the spectral changes in the remaining region (300–500 nm)
is nearly same as observed for 2 when dilute solution of 1 was
employed. This shows the progressive oxidation of VIVO species and
the formation of a oxidoperoxidovanadium(V) complex possibly
0.8
1.00
(a)
400 nm
0.30
(b)
0.6
0.75
0.50
0.25
0.00
0.15
0.00
312 nm
0.4
785 nm
350 400 450 500
400 nm
0.2
0.0
600
700
800
900
1000
1100
300
350
400
450
500
Wavelength (nm)
Wavelength (nm)
Fig. 10. UV–vis spectral changes observed during titration of K[VVO2(sal-iah)]·H2O (2) with H2O2. (a) The spectra recorded after successive addition of one drop portions of
dilute H2O2 (2 drops of 30% H2O2 in 5 mL MeOH) to 50 mL of 4.0 × 10−5 M solution of (2). (b) The spectra recorded after successive addition of one drop portions of dilute
H2O2 (3 drops of 30% H2O2 in 10 mL DMSO) to 50 mL of 2.4 × 10−2 M DMSO solution of [VIVO(sal-iah)(H2O)] (1).

M.R. Maurya, N. Kumar / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 172–181
181
via dioxidovanadium(V) species. The oxidoperoxido species then
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2315–2344.
Dibasic tridentate ONO donor ligand H2sal-iah derived from
salicylaldehyde and indole-3-acetic hydrazide has been used
to prepare oxidovanadium(IV) and dioxidovanadium(V) com-
plexes, [VIVO(sal-iah)(H2O)] (1) and K[VVO2(sal-iah)]·H2O. These
complexes upon treatment with H2O2 in methanol gave same oxi-
doperoxido species in solution. These complexes have also been
grafted successfully through covalent bonding of the nitrogen of the
indole group to chloromethylated polystyrene cross-linked with 5%
divinylbenzene where 1 retains the same structure in PS-[VIVO(sal-
iah)(H2O)] (3) while 2 changes to PS-[VVO(OMe)(sal-iah)] (4).
The polymer-grafted complex 4 catalyzes the oxidation of
styrene and cyclohexene efficiently in the presence of H2O2. As high
as 95% conversion of the styrene with styrene oxide, benzaldehyde,
benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde
as major products were obtained under the optimized reaction
conditions. Oxidation of cyclohexene gave 96% conversion with
cyclohexene oxide, 2-cyclohexen-1-ol, cyclohexane-1,2-diol and 2-
cyclohexen-1-one as the major products. The presence of some of
the metal centers on the surface of the polymer, supported by EDX
study, due to insertion of spacer between polymer support and cat-
alyst possibly allowed their better interaction with substrates and
oxidant during catalytic reaction resulting in better performance
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MRM thanks the Department of Science and Technology, the
Government of India, New Delhi for financial support (grant no.
SR/S1/IC-32/2010) of the work. NK acknowledges Council of Scien-
tific and Industrial Research, New Delhi for fellowship. Authors are
also thankful to Prof. J. Costa Pessoa for help in recording EPR and
51V NMR spectra reported in this paper.
Appendix A. Supplementary data
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Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2013.12.006.